In wireless communication, in the case of radar installations or other receiving devices which operate at microwave frequencies, and whose input is normally coupled to an antenna, high-power interference pulses or frequency bursts, with steep rising flanks can deliberately or inadvertently be applied to the input of the appliance, whose frequencies fall in the operating frequency range of the appliance, where they temporarily or permanently affect the sensitive input stages or, furthermore, cause damage.
In the past, it has therefore variously been proposed that appliance inputs such as these be protected by means of protective circuits upstream of the input, which reliably limit or attenuate such fast high-power interference pulses without noticeably impeding the wanted signals being fed into the appliance input. In this case, a plurality of limiter circuits, which cover a coarse and a fine range of the interference power, are frequently connected in series, for example with gas discharge paths being used for the coarse range and limiting semiconductor components being used for the fine range.
By way of example, CH-A5-654 149 discloses a protective circuit against NEMPs, in which a gas cell as coarse protection means and a varistor as fine protection means are connected in series via a frequency-selective delay element.
DE-A1-34 25 296 discloses a protective apparatus for electronic appliances, in which a coarse protective device with a gas discharge path and a fine protective device which operates with semiconductor elements are accommodated in separate housings and are connected to one another via a relatively long connecting cable. DE A1-36 26 800 also discloses a comparable solution.
DE A1-39 07 199 discloses an overvoltage protective device for coaxial cables, in which a three-electrode suppressor is used for coarse protection, and a combination of switching diodes and limiter diodes is used for fine protection. The three-electrode suppressor is inserted into a printed circuit board on which the other circuit elements are also arranged. The end-face electrodes of the three-electrode suppressor are connected to the inner conductor and outer conductor of the coaxial cable, while the center electrode is connected to a separate ground line.
EP-A1-0 855 758 discloses a circuit arrangement for protection of RF input circuits of telecommunication appliances, in which a fine protective circuit having a varistor and a limiter diode is provided behind a gas capsule suppressor or a lambda/4 short-circuit line.
Finally, it has been known for a long time for PIN diodes to be used for limiting interference pulses at the input of appliances which operate in the microwave range, and these are distinguished by very small internal capacitances and short response times (see for example U.S. Pat. No. 5,345,199 or WO-A1-2006/124104).
Other protective methods relate to quick active regulation of a limiting element in the input of the appliance (US-A1-2006/0293020).
The known protective circuits and protective methods are not sufficient for reliably limiting or attenuating very high power interference pulses, for example those transmitted by pulsed radars or specific interference pulse generators.